The invention relates to a method and an apparatus for priming an extracorporeal blood circuit.
Specifically, though not exclusively, the invention is usefully applied for priming a dialysis set.
U.S. Pat. No. 4,707,335 describes a system for disinfection and reuse of a membrane separator for blood treatment and fluid transport lines associated to the separator. The system comprises a manifold defining internally a cavity and externally two connectors connected to the patient end of an arterial blood line and a venous blood line, so that the blood lines are intercommunicating with each other, forming a closed fluid circuit in which a disinfecting solution can be made to circulate, for reuse purposes.
U.S. Pat. No. 5,948,251 describes a dialysis machine provided with a disinfection port, a discharge port and a blood pump. Also described is a process for disinfecting a blood tubing set which includes connecting an end of the blood tubing set to the disinfection port and an opposite end thereof the discharge port. The blood tubing set is coupled to the blood pump which pumps the disinfecting solution from the disinfection port to the discharge port.
WO 96/40320 describes a priming method according to which, before the treatment a disposable blood tubing set and a dialyser (new or used) are attached to a dialysis machine and prepared by an operator for use on a patient. The blood tubing set and the dialyser are filled with a sterile saline solution to remove the air from the extracorporeal circuit and to rinse same. To guarantee complete removal of the all traces of undesirable substances from the membrane, the saline solution is recirculated through the dialyser for a predetermined period of time. The recirculating further guarantees that any excess air remaining in the circuit is expelled before connecting the circuit itself to the patient. The blood tubing set comprises a T or Y connector for connecting the two patient ends of the arterial and venous lines to a discharge port connected to a discharge line which is in turn connected to a drainage system. The discharge line can be part of the dialysis machine discharge circuit, i.e. the circuit connecting the outlet of the exhausted dialyser liquid of the dialyser to the drainage system, or can be a line which is separate from the above-cited discharge circuit. The drainage system is the same that receives the used dialysis fluid from the dialysis machine during the treatment. A discharge valve selectively opens or closes the discharge line. The discharge valve can be operated manually or can be controlled by the control unit of the dialysis machine. In the initial priming configuration, an end of the T or Y connector is sealedly coupled with the discharge port, while the other two ends are coupled to the arterial and venous lines. A bag of saline solution is connected to a service line connected to the arterial blood chamber. The venous and arterial lines are closed by respective clamps which can be controlled by the control unit of the dialysis machine. A vent valve in the arterial blood chamber is opened (manually or by means of an automatically-commanded valve) in order to allow the chamber to fill by force of gravity with the saline solution dropping from the bag. When the arterial chamber is full of the saline solution, the vent is closed and the automatic priming process can begin. The arterial clamp is opened for a predetermined time to enable the tract of arterial line comprised between the arterial chamber and the patient arterial end connected to the discharge port to fill with saline solution. Then the arterial clamp is closed, the venous clamp opened, and the blood pump begins to rotate (forward, i.e. in the rotation direction which it normally has during the treatment) in order to fill the rest of the extracorporeal circuit with saline solution from the bag. Once the circuit is filled, the discharge valve is closed, the arterial clamp opened and the blood pump made to rotate backwards (in the opposite direction to its normal direction during treatment) in order to cause the saline solution to circulate through the extracorporeal circuit. During this phase any air left in the blood compartment of the dialyser is transferred into the arterial chamber and remains there in the upper part of the chamber. Thereafter the blood pump is rotated forwards for a further recirculating stage during which the ultrafiltration system of the dialysis machine generates an ultrafiltration flow through the membrane, from the blood compartment to the dialyser compartment of the dialyser in order to guarantee the cleanliness of the membrane. After the patient has been connected to the extracorporeal circuit, the Y or T connector is removed.
One of the drawbacks of the method described in WO 96/40320 is the risk of contamination of the extracorporeal blood circuit by contaminating agents originating from the discharge port, especially in the recirculating stage.
A further drawback consists in the special care and attention the operator must take during the apparatus readying stage of the apparatus in the priming configuration, with a consequent increase in work times, extra work for the operator, the need to have well-trained operators and the risk of error.